This project is concerned with the etiology of oral ulcerations produced by - 1) primary and recurrent herpes, 2) recurrent aphthous ulcers. The objectives of the project are: (1) To establish the salient clinical features of these diseases for differential diagnosis; (2) to establish the histopathologic aspects of the oral ulcerations; (3) to establish the role of predisposing factors in the etiology of these diseases; (4) to investigate the mechanism which governs recurrence; (5) to establish the use of laboratory procedures as an aid in diagnosis; (6) to identify and characterize the etiologic agent(s) and histopathologic mechanism in these diseases.